A low temperature surface of a Cryogenics pump is placed in a vacuum chamber. Gas molecules are condensed and adsorbed on the low temperature surface and are captured by the low temperature surface, in the vacuum chamber. Thus, the cryogenics pump is a vacuum pump for evacuating the gas molecules. Generally, a small closed cycle helium refrigerator is used to obtain the low temperature surface.
It is a regenerator based refrigerator in which helium gas is used as refrigerant gas or operating gas. The compressed helium gas is transferred into the cold expansion space in the cold end and it is adiabatically expanded to obtain low temperature. The regenerator based refrigerator is characterized in that it is provided with a heat exchanger cooled as regenerator material which functions to extract heat from high temperature and pressure helium gas, flowing in one direction, to reserve heat and precool the helium gas to be transferred into the expansion space. It functions to warm the helium gas of low pressure and low temperature, flowing in the opposite directions prior to returning to the ambient temperature space.
The regenerator contains regenerator material which exchanges heat with the helium gas. Pb is used as regenerator material, which has high thermal conductivity and higher specific heat than any other metals at low temperature (under 30 k), and it is less expensive.
In some refrigerators of high capacity, magnetic material such as Er3Ni, whose specific heat is higher than Pb at a very low temperature (under 15 k), is used. For example, refer to patent document 1 and patent document 2.
Patent Document 1: JP10-300251A
Patent Document 2: JP2004-143341A